ES2260383T5 - DEVICE AND PROCEDURE FOR THE EXTRUSION OF POLYETHYLENTEREFTALATE. - Google Patents

Abstract

Polyethyleneterephthalate extrusion equipment of material in granule form, still humid, coming from both ground recovered products and also virgin material, comprising a chassis (29), containing a co-rotating, oil-thermoregulated extruder with two screws (31, 32), which comprises a first zone (A), equipped with an opening (34) where there is an aspiration hood (35) for a first "open top" degassing, a second zone (C) where there is at least one stack (37, 38) for a further degassing, between the two zones (A, C), there being a tight zone (B), and a carrying and loading zone (E) activated by the screws (31, 32). The description also relates to an extrusion process of polyethyleneterephthalate effected in a co-rotating twin-screw extruder which comprises in a first zone (A) an "open top" degassing phase, followed by a stack (37, 38) degassing phase, between the two phases there being a tight zone which does not deteriorate the material, followed by a carrying, loading and amalgamation phase of the molten material and a final pumping phase with the extrusion of polyethyleneterephthalate. <IMAGE>

Description

The present invention relates to a device and a process for the extrusion of polyethylene terephthalate.

Polyethylene terephthalate (PET) is an extremely hygroscopic material; the manufacturers condition and market it in the form of granules, with a degree of humidity equal to approximately 2,000 parts per million.

Before it can be extruded, it is first dehumidified at 160 ° C for 6 hours, in order to remove moisture internally and externally incorporated in each granule to reach 20 parts per million. Under these conditions, the material cannot be extruded without hydrolyzing and so as to maintain a characteristic intrinsic viscosity.

Traditional dehumidification procedures occur in most cases before the extrusion stage with single spindles and turn out to be complex and expensive.

This traditional dehumidification procedure consists in maintaining an amount of material equal to the extruder's productive rate (kg / h) for 6 hours in a silo, and passing moisture free air through it, with considerable energy consumption.

In addition, it should be considered that, when PET comes from the recovery of used bottles that have been ground and / or thinly milled sheets that derive from residual products of thermoforming of trays and blister packs, dehumidification is particularly complex.

This material, in fact, above a temperature of 80 ° C tends to soften and, if it is not in the form of granules, as in the present case, it conglomerates and can no longer be handled, unless its apparent weight is increased by means of an additional densification procedure.

US-A-4,107,787 refers to a spindle extruder for the continuous processing and degassing of elastomers and polymers having a plurality of degassing zones and in which two spindles that can rotate in opposite directions are mounted. The preamble of claim 1 part of this prior art document. US-A-5,728,337 refers to a twin screw extruder and an extrusion process using this extruder for a resin material containing a fine filler with a high mixing ratio to the resin material.

The objective of the present invention is to produce equipment that overcomes the technical problems described above.

Another objective is to produce a particularly simple and limited cost equipment, which allows for optimal extrusion.

An additional objective, of course, is to be able to produce polyethylene terephthalate (PET) without the need to dehumidify and densify the ground product.

These objectives according to the present invention are achieved by means of a device for the extrusion of polyethylene terephthalate according to claim 1, and a method thereof according to claim 6.

Other features of the invention are indicated in the subsequent claims.

The characteristics and advantages of a set of equipment for the extrusion of polyethylene terephthalate according to the present invention can be understood more clearly from the following illustrative and non-limiting description, which refers to the attached schematic drawings, in which:

Figure 1 is a side elevational view of a schematic plan illustrating a method according to the known technique,

Figure 2 shows an elevation view of a twin-screw corrotative extruder according to the present invention, schematically and partially in section,

Figure 3 is a schematic cross section of the two spindles of the twin screw extruder,

Figure 4 is an enlarged section of an upper part of the extruder,

Figures 5, 6 and 7 are enlarged views of details of a section of the extruder illustrated in Figure 4.

With reference to Figure 1, this illustrates a schematic plan showing a procedure according to the known technique, previously described.

The figure shows how the polyethylene terephthalate (PET) ground in granules and from the recovery of bottles, residual sheets of the thermoforming, etc., is fed by means of a conveyor belt 11 towards a densidifying group indicated with reference number 12, of the which in turn is sent through a conduit 13 to a silo container 14.

The material is subsequently sent, by means of an additional duct 15, to a hopper 16 in which it is maintained for approximately 6 hours at a temperature of 160 ° C. The hopper is coupled to a dehumidifying group 17 that allows maintaining this temperature inside the hopper 16.

In parallel, polyethylene terephthalate (PET) as a virgin material in granular form is fed through pipes 18 to a hopper 19 in which it is maintained for approximately 6 hours at a temperature of 160 ° C. The hopper 19 is also coupled to a dehumidifier group 20 which allows this temperature to be maintained inside the hopper 19. A pipe 21 leaving the hopper 19 is connected to an additional hopper 22 to feed a twin-screw corrotative extruder. 23 of the known type.

A second pipe 24 is connected to the hopper 16 and receives the densified and dehumidified milled recovered material that must be loaded inside the extruder 23, together with the pattern fed from an additional hopper 25.

Therefore, it may be indicated that particularly complex dehumidification steps must be carried out that create the problems of the known technique indicated above.

Figures 2 to 7 illustrate a twin-screw corrotative extruder, indicated globally with reference number 30, which forms the equipment object of the present invention.

The spindles 31 and 32, which are rotational in the same rotational direction, are located in this extruder 30 inside a chassis 29. The polyethylene terephthalate material in the form of granules, still wet, from recovery products and virgin material , is fed through a feed inlet 33. This material, according to the invention, is treated between the two spindles 31 and 32 so as to advance inside the extruder, which is, for example, thermoregulated with oil. .

After a certain section inside the body of the extruder 30, there is an opening 34 in a first zone A, in correspondence with which is a suction bell 35 which carries out a degassing called "open cover" or degassing environmental. This suction hood 35 is under a slight vacuum to prevent the material (granules / sheets), which in this position of the extruder indicated above is not yet molten, but only sintered, from being damaged. The material, in fact, only partially fills the air gaps of the spindles 31, 32 and any possible strong vacuum could extract a part of it.

Next, inside the extruder 30, in a second rear zone B, there is a series of parts that act as a seal. This zone B consists of the presence of a series of cams 36, arranged on the spindles 31, 32, which are loaded with almost molten material and under light pressure. This prevents the strong vacuum of the subsequent degassing groups described below, influencing the environmental degassing indicated above.

A first chimney 37 is, in fact, located in an area C, followed a short distance by a second chimney 38, in an additional zone D, both for further degassing. These two chimneys carry out a degassing in tandem which, for example, in an extruder with a length ratio of 34 to 42 diameters, can be found at a distance between the two chimneys of approximately 6/9 diameters.

Internally, the spindle is constructed so that it is only partially filled with molten material and exposes the material under treatment to the crushing and calendering action for a long time. In this way, the entire mass is subjected to the aspiration action of the vacuum effect created in this way.

This degassing has the specific function of eliminating evaporated water contained in the material.

Next, the extruder 30 continues with an additional zone E in which the transport and loading is carried out, activated by the spindles 31 and 32.

Finally, an end zone F of the extruder 30 activates the final pumping of the material produced with said process.

This series of steps that are carried out in the extruder of the present invention thus allow to treat a wet granular material, avoiding complicated dehumidification operations.

In said process, in fact, polyethylene terephthalate (PET) material is fed into granules, both from virgin material and also from the milling of recovered products, in a double-screw corrotative extruder in its current state, that is, containing moisture.

After loading a mixture of the two types of material specified above, an environmental degassing stage occurs in a first zone provided with a suction hood, followed by a

10 additional degassing by at least one chimney. Between the two stages, a hermetic zone is necessary, inside the apparatus, so as not to influence the two stages and not to damage the material in production.

In particular, this additional stage of degassing is carried out by means of two tandem chimneys to optimize the operation.

A transport and loading stage is then carried out, which facilitates the amalgam of the molten material, followed by a final pumping stage, obtaining the extrusion of the polyethylene terephthalate (PET) that derives from the granules of both the virgin material and the material from the grinding of the recovered products.

The problems of the known technique indicated above are solved in this way by eliminating the dehumidification stages and the equipment associated therewith, with a considerable saving of resources and operating time.

Claims (6)

one.

Polyethylene terephthalate extrusion equipment in the form of granules, in particular for wet granules, from both milled recovered products and virgin material, comprising a chassis (29), which contains a thermo-regulated oil extruder with two spindles (31 , 32), said extruder having a feed inlet (33) for the material in the form of granules and comprising a plurality of degassing zones A, C, D provided with openings (34, 35; 37, 38), an area airtight (B) and a transport and load zone (E) activated by said spindles (31, 32), characterized in that the two spindles (31, 32) of said extruder are corrotative in the same rotational direction and because a first zone Degassing (A) is provided with a suction hood (35) towards the environment, a second degassing zone (C and D) is provided with two chimneys (37, 38) in tandem, being positioned between said prime ra and second degassing zones (A; C and D) a hermetic zone (B) to prevent deterioration of the material in production.

2.

Extrusion equipment according to claim 1, characterized in that it comprises an additional final zone (F) that activates the final pumping of the material produced with said equipment.

3.

Extrusion equipment according to claim 1, characterized in that said hermetic zone (B) is produced by a series of cams (36) arranged in said spindles (31, 32) that are loaded with almost molten material and under light pressure.

Four.

Extrusion equipment according to any of the preceding claims, characterized in that said extruder has a length ratio of 34 to 42 diameters.

5.

Extrusion equipment according to claim 1, characterized in that in said extruder the two chimneys (37, 38) that carry out a tandem degassing, are at a distance of approximately 6/9 diameters.

6.

Procedure for the extrusion of polyethylene terephthalate that uses as a granule-shaped material a wet granulate, coming from both milled recovered products and virgin material that is carried out in a twin-screw extruder divided into a plurality of zones (A, C, D) having openings (34, 35; 37, 38), said process comprising successive degassing stages in different zones, a transport and loading stage, followed by a final pumping stage in which the extrusion of the polyethylene terephthalate is obtained, characterized in that said procedure, which is carried out in a double-screw corrotative extruder in which the spindles rotate in the same rotational direction comprises a first stage of degassing of a material in the form of granules in a first zone (A) provided with a bell of aspiration (35) towards the environment, followed by a second stage of degassing in a successive zone (C and D) by means of d The chimneys (37, 38) in tandem, said first and second stages of degassing being hermetically separated to avoid deterioration of the material in production.